190 research outputs found
Influence of carrier concentration on properties of InAs waveguide layers in interband cascade laser structures
The work has supported by the European Commission within the Project WideLase (No. 318798) of the 7-th Framework Programme and by the National Science Center of Poland by the Grant No. 2014/15/B/ST7/04663.We present a characterization of doped InAs layers in interband cascade lasers exploiting the plasmon-enhanced waveguiding. Fast differential reflectance was employed in order to identify the plasma-edge frequency via the Berreman effect and shown as an advantageous method when compared to other types of measurements. The carrier concentration was then derived and compared with the nominal doping densities. The emission properties of the investigated structures were studied by means of photoluminescence (PL). Its full-width at half-maximum and integrated intensity were extracted from PL spectra and analyzed in the function of the doping density (carrier concentration). The PL linewidth was found to be independent of the carrier concentration indicating an insignificant contribution of doping to the structural properties deterioration. The PL intensity decay with the carrier concentration suggests being dominated by Auger recombination losses.PostprintPeer reviewe
Controlled lasing from active optomechanical resonators
Planar microcavities with distributed Bragg reflectors (DBRs) host, besides
confined optical modes, also mechanical resonances due to stop bands in the
phonon dispersion relation of the DBRs. These resonances have frequencies in
the sub-terahertz (10E10-10E11 Hz) range with quality factors exceeding 1000.
The interaction of photons and phonons in such optomechanical systems can be
drastically enhanced, opening a new route toward manipulation of light. Here we
implemented active semiconducting layers into the microcavity to obtain a
vertical-cavity surface-emitting laser (VCSEL). Thereby three resonant
excitations -photons, phonons, and electrons- can interact strongly with each
other providing control of the VCSEL laser emission: a picosecond strain pulse
injected into the VCSEL excites long-living mechanical resonances therein. As a
result, modulation of the lasing intensity at frequencies up to 40 GHz is
observed. From these findings prospective applications such as THz laser
control and stimulated phonon emission may emerge
Observation of the transition from lasing driven by a bosonic to a fermionic reservoir in a GaAs quantum well microcavity
We show that by monitoring the free carrier reservoir in a GaAs-based quantum well microcavity under non-resonant pulsed optical pumping, lasing supported by a fermionic reservoir (photon lasing) can be distinguished from lasing supported by a reservoir of bosons (polariton lasing). Carrier densities are probed by measuring the photocurrent between lateral contacts deposited directly on the quantum wells of a microcavity that are partially exposed by wet chemical etching. We identify two clear thresholds in the input-output characteristic of the photoluminescence signal which can be attributed to polariton and photon lasing, respectively. The power dependence of the probed photocurrent shows a distinct kink at the threshold power for photon lasing due to increased radiative recombination of free carriers as stimulated emission into the cavity mode sets in. At the polariton lasing threshold on the other hand, the nonlinear increase of the luminescence is caused by stimulated scattering of exciton-polaritons to the ground state which do not contribute directly to the photocurrent.PostprintPeer reviewe
Single-photon emission of InAs/InP quantum dashes at 1.55 μm and temperatures up to 80 K
This research was supported by the National Science Center of Poland within Grant No. 2011/02/A/ST3/00152.We report on single photon emission from a self-assembled InAs/InGaAlAs/InP quantum dash emitting at 1.55 µm at elevated temperatures. The photon auto-correlation histograms of the emission from a charged exciton indicate clear antibunching dips with as-measured g(2)(0) values significantly below 0.5 recorded at temperatures up to 80 K. It proves that charged exciton complex in a single quantum dash of the mature InP-based material system can act as a true single photon source up to at least liquid nitrogen temperature. This demonstrates the huge potential of InAs on InP nanostructures as non-classical light emitters for long-distance fiber-based secure communication technologies.PostprintPublisher PDFPeer reviewe
Conditional phase shift from a quantum dot in a pillar microcavity
Large conditional phase shifts from coupled atom-cavity systems are a key
requirement for building a spin photon interface. This in turn would allow the
realisation of hybrid quantum information schemes using spin and photonic
qubits. Here we perform high resolution reflection spectroscopy of a quantum
dot resonantly coupled to a pillar microcavity. We show both the change in
reflectivity as the quantum dot is tuned through the cavity resonance, and
measure the conditional phase shift induced by the quantum dot using an ultra
stable interferometer. These techniques could be extended to the study of
charged quantum dots, where it would be possible to realise a spin photon
interface
Two-photon interference from remote quantum dots with inhomogeneously broadened linewidths
This work was financially supported by the German Ministry of Education and Research (BMBF) via the project QuaHL-Rep and by the State of Bavaria.In this paper, we study the influence of quasiresonant and nonresonant excitation on the interference properties of single photons emitted from quantum dots (QDs). The quasiresonant excitation scheme leads to an increase of interference visibility of photons emitted from the same QD to 69% compared to 12% for nonresonant excitation. Furthermore, we demonstrate quantum interference of photons emitted from separate QDs which are simultaneously excited into their p shell. We can readily extract a two-photon interference visibility as high as (39 ± 2)% for nonpostselected coincidences exceeding the predicted value based on coherence and radiative decay times of the quantum dot emission (similar to 25%). We account for this observation by treating the emission of both quantum dots as inhomogeneously broadened ensembles of Fourier-limited photons and observe good congruence between experiment and model.Publisher PDFPeer reviewe
Half adder capabilities of a coupled quantum dot device
We gratefully acknowledge nancial support from the European Union (FPVII, 2007- 2013) under grant agreement no 256959 NANOPOWER and grant agreement no 318287 LANDAUER as well as from the state of Bavaria.In this paper we demonstrate two realizations of a half adder based on a voltage-rectifying mechanism involving two Coulomb-coupled quantum dots. First, we examine the ranges of operation of the half adder's individual elements, the AND and XOR gates, for a single rectifying device. It allows a switching between the two gates by a control voltage and thus enables a clocked half adder operation. The logic gates are shown to be reliably operative in a broad noise amplitude range with negligible error probabilities. Subsequently, we study the implementation of the half adder in a combined double-device consisting of two individually tunable rectifiers. We show that this double device allows a simultaneous operation of both relevant gates at once. The presented devices draw their power solely from electronic fluctuations and are therefore an advancement in the field of energy efficient and autonomous electronics.PostprintPeer reviewe
Controlling circular polarization of light emitted by quantum dots using chiral photonic crystal slab
We study the polarization properties of light emitted by quantum dots that
are embedded in chiral photonic crystal structures made of achiral planar GaAs
waveguides. A modification of the electromagnetic mode structure due to the
chiral grating fabricated by partial etching of the wave\-guide layer has been
shown to result in a high circular polarization degree of the quantum
dot emission in the absence of external magnetic field. The physical nature of
the phenomenon can be understood in terms of the reciprocity principle taking
into account the structural symmetry. At the resonance wavelength, the
magnitude of is predicted to exceed 98%. The experimentally achieved
value of % is smaller, which is due to the contribution of
unpolarized light scattered by grating defects, thus breaking its periodicity.
The achieved polarization degree estimated removing the unpolarized nonresonant
background from the emission spectra can be estimated to be as high as 96%,
close to the theoretical prediction
Temperature dependency of the emission properties from positioned In(Ga)As/GaAs quantum dots
The authors gratefully acknowledge funding by the state of Bavaria and the bilateral project of the Deutsche Forschungsgemeinschaft (DFG) and the Japan Science and Technology Agency (JST) (project ‘single quantum dot lasers’).In this letter we study the influence of temperature and excitation power on the emission linewidth from site-controlled InGaAs/GaAs quantum dots grown on nanoholes defined by electron beam lithography and wet chemical etching. We identify thermal electron activation as well as direct exciton loss as the dominant intensity quenching channels. Additionally, we carefully analyze the effects of optical and acoustic phonons as well as close-by defects on the emission linewidth by means of temperature and power dependent micro-photoluminescence on single quantum dots with large pitches.Publisher PDFPeer reviewe
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